Why not just "fd -e fi.md -X batcat"?
That's not what I'm after. I want to survey the whole page with my eyes as fast as possible for unusual colors / oddly short files / etc, then press `q` to have the screen totally clear and move on to the next one.
The default (/usr/bin/lesspipe.sh, shipped with less) isn't very clever. It can uncompress files in some common formats and open images, but isn't very smart and doesn't handle markdown or code of any kind as far as I can tell.